Data compression is utilized in data handling processes, where too much data is present for practical applications using the data. Commonly, compression is used in communication links, to reduce the transmission time or required bandwidth. Similarly, compression is preferred in image storage systems, including digital printers and copiers, where “pages” of a document to be printed are stored temporarily in precollation memory. The amount of media space on which the image data is stored can be substantially reduced with compression. Generally speaking, scanned images, i.e., electronic representations of hard copy documents, are often large, and thus make desirable candidates for compression.
Generally, an image does not change very much on a pixel to pixel basis and therefore has what is known as “natural spatial correlation”. In natural scenes, correlation is generalized, but not exact. Noise makes each pixel somewhat different from its neighbors, but the natural spatial correlation enables not only the compression of digital image data, but the performance of certain image processing operations on the compressed data. Contrariwise, in synthetic graphics and computer-generated text, the correlation tends to be much higher, with colors limited to a small set. The limited set of colors and high correlation make these image types good candidates for lossless compression, at possibly higher compression ratios than those achievable with lossy compression schemes.
Spatial uniformity correction via spatially varying tone reproduction curves (TRCs) and spatial N-dimensional color transformations have been demonstrated to be very effective for streak compensation on several print engines. However, current implementations apply to uncompressed image data. It is desirable to enable streak compensation on compressed images. For some products, it may be advantageous to perform the compensation in the digital front end (DFE), where the image data is compressed. Also, applying compression in the DFE can save significant hardware costs.
Some implementations carry the compressed image data further down the image path. The present disclosure will be described in connection with particular lossy (i.e. JPEG, and JPEG2000 encoded image data), compression embodiments. The disclosure will also be described in connection with run length encoded image data (i.e. compressed line work). The present disclosure presents a streak compensation method and print system for several forms of compressed image data types utilized by various image marking engines.